Windows 10 is on pace to power 20% of all Windows desktop systems by the end of June, or around the time Microsoft issues its next major upgrade, according to data published this week.

Data from U.S.-based analytics vendor Net Applications pegged Windows 10's user share -- a proxy for the percentage of personal computers worldwide that ran the OS -- at 15.3% in April, a 1.2-percentage point increase from the month prior. Net Applications tallied unique visitors to clients' websites to come up with its measurements.

The new operating system's growth last month was smaller than in January and March of this year, but larger than February's.

Windows 10's adoption has consistently been stronger in the U.S. than the global average. (Data: StatCounter, Digital Analytics Program.)

Windows 10 accounted for about 17.3% of all Windows; the difference between its user share of all PCs and only those running a version of Windows stemmed from the fact that Windows ran 89% of all personal computers, not 100%.

Using Net Applications' data for the last 12 months, Computerworld calculated that Windows 10's growth line should crack the 20% mark by the end of June, when it will power just over 300 million machines.

Microsoft intends to release the year's major upgrade to Windows 10, dubbed "Anniversary Update," this summer. While it has not yet set a specific launch date, it will presumably ship the upgrade before the one-year point, or July 29.

Windows 10 now powers approximately 259 million systems, according to Computerworld's analysis using Net Applications' numbers and Microsoft's oft-cited claim that 1.5 billion machines run Windows. That would represent an increase of about 24 million in April, or less than 1 million each day.

In late March, Microsoft claimed that 270 million customers ran Windows 10 at least once in the past month. However, the Redmond, Wash., company's number included tablets, smartphones, video game consoles and other devices that either run Windows 10 or a variant, while Net Applications' included only personal computers.

Other data sources told a comparable tale.

Irish analytics firm StatCounter put Windows 10 at 17.9% of all personal computers for April, a 1.4-percentage point gain. StatCounter measured global usage share -- more a metric for activity rather than users -- and although its estimate for Windows 10 was larger than Net Applications', their month-over-month rate of increase was similar (StatCounter's was 9%, Net Applications', 11%).

In the U.S., Windows 10 continued to perform better than globally. According to the Digital Analytics Program (DAP), Windows 10 accounted for 23.7% of all Windows PCs, an increase of 2.8 percentage points over March, for a month-over-month growth rate of 13%.

DAP tracks visits to more than 4,000 websites on over 400 different domains maintained by U.S. government agencies, so its data is highly U.S.-centric.

Most other editions of Windows stuck to long-established trends: Windows XP's global share of all Windows PCs slipped slightly to 12%, and Windows 7's user share dropped to 54% of all Windows machines. But the combined share of Windows 8 and 8.1 climbed to 15% in April, an unusual uptick that may be less a signal of a renaissance of those 2012-2013 operating systems and more an aberration in Net Applications' data tracking.

Meanwhile, Net Applications claimed that Apple's OS X -- perhaps soon to be rebranded MacOS -- jumped to 9.6% of all personal computers worldwide, an unprecedented increase, while Windows fell under 90% for the first time to land at 88.8%.

Both those numbers were questionable simply because they pointed to extraordinary one-month changes. The previous record for a one-month increase in OS X, for example, was just one-third the size that Net Applications asserted for April.